Effects of 1-methylcyclopropene on function of flag leaf and development of superior and inferior spikelets in rice cultivars differing in panicle types

High ethylene production usually slackens spikelets development in compact panicled rice (Oryza sativa L.) cultivars. 1-Methylcyclopropene (1-MCP) is a potent inhibitor of ethylene action that has been shown to prevent ethylene-induced effects in fruits. However, effects of 1-MCP on spikelets development in rice cultivars differing in panicle types are unclear. This study explored whether 1-MCP is involved in regulating rice flag leaf function, and superior and inferior spikelets development. Four rice cultivars were field grown in 2012 and 2013, including two lax-panicled cultivars, Liangyoupeijiu (LYP9) and Guodao 6 (GD6), and two compact-panicled cultivars, Yongyou 9 (YY9) and Yongyou 12 (YY12). Results showed that 1-MCP played a positive role in regulating photosynthetic rate of rice flag leaf. Application of 1-MCP was more effective on enhancing grain filling rate of LYP9, GD6, and YY9. 1-Aminocyclopropane-1-carboxylic acid synthase (ACS) activity and ethylene production of inferior spikelets were more sensitive to the regulation of 1-MCP comparing to that in superior spikelets. Compared to other cultivars, ACS activity and ethylene production in inferior spikelets of LYP9 with 1-MCP treatment were significantly lower than that in control (CK). Effect of 1-MCP on starch content in superior and inferior spikelets varied with rice cultivars, but application of 1-MCP significantly enhanced starch content of inferior spikelets for LYP9. To compare with CK, application of 1-MCP greatly increased grain yield, spikelet fertility, and harvest index for LYP9, GD6, and YY9, especially for LYP9. Results indicate that 1-MCP favorably regulated flag leaf photosynthesis and inferior spikelets development in rice cultivars used in this trial, and LYP9 showed the best performances after application of 1-MCP.